1. Field of the Invention
This invention relates to an X-ray image photographing apparatus for effecting photographing by the use of a grid, and a grid device.
2. Related Background Art
When radiation such as X-ray, α-ray, β-ray, γ-ray, an electron beam or an ultraviolet ray is applied to a certain kind of fluorescent material, part of this radiation energy is accumulated in the fluorescent material. It is known that excitation light such as visible light may be applied to this fluorescent material, whereby the fluorescent material exhibits accelerated light emission in conformity with the accumulated energy. The fluorescent material exhibiting such a nature is called an accumulative fluorescent material or an accelerative fluorescent material.
Heretofore, by the utilization of this accumulative fluorescent material, the radiation image information of an object such as a human body has been once recorded on a sheet of accumulative fluorescent material, and this sheet of accumulative fluorescent material has been scanned by the use of excitation light such as a laser beam to thereby emit accelerated light, and the obtained accelerated light has been read to thereby obtain an image signal. A radiation image information recording-reproducing system for outputting the radiation image of the object as a visible image to a recording material such as a photosensitive material or a display apparatus such as a CRT on the basis of this image signal is proposed, for example, by Japanese Patent Application Laid-Open No. 55-12429, Japanese Patent Application Laid-Open No. 56-11395, etc.
Also, in recent years, an apparatus using a semiconductor sensor to likewise photograph an X-ray image has been developed. These systems, as compared with a conventional radiation photographic system using silver salt photographs, have the practical advantage that an image can be recorded over a very wide range of radiation exposure area. That is, X-rays in a very wide dynamic range are read by photoelectric converting means and converted into an electrical signal. By the use of this electrical signal, the radiation image is outputted as a visible image to the recording material such as a photosensitive material or the display apparatus such as a CRT, whereby there can be obtained a radiation image which is not affected by the fluctuation of a radiation exposure amount.
However, in the analog photographing using the accumulative fluorescent material shown in the above-described example of the prior art, use is made of various grids for decreasing scattered rays during photographing, but in digital photographing using a semiconductor sensor, moiré fringes are created from the relation between the sampling pitch and the frequency of the grid, and in an apparatus, a plurality of kinds of grids or an image by without a grid is not supported.